Diesel engines designed for marine and stationary power applications can be either 2-stroke or 4-stroke cycle having up to 20 cylinders and are typically classified as low-speed, medium-speed or high-speed diesel engines. These engines burn a wide variety of fuels ranging from residual or heavy fuel oils to natural gas (diesel compression or spark-ignited) and are most commonly used for marine propulsion, marine auxiliary (vessel electricity generation), distributed power generation and combined heating and power (CHP). Lubrication of such engines can be all-loss (i.e., lubricant fed directly to the cylinder by cylinder oil) or recirculation involving oil sumps. Lubrication of critical engine parts includes piston rings, cylinder liners, bearings, piston cooling, fuel pump, engine control hydraulics, etc. Fuel is typically the major cost of operating these engines and a typical 12 cylinder, 90 cm bore low-speed diesel engine used in marine vessel container service will burn up to approximately $7M of heavy fuel oil or $14M of marine diesel fuel per year. Therefore, a fuel efficiency gain of as little as 1% would result in approximately $130K to $200K in annual savings to the ship operator. In addition, governmental organizations, such as the International Marine Organization, U.S. Environmental Protection Agency and the California Air Resources Board are legislating emissions requirements for these engines. Improving fuel efficiency will not only reduce operating cost, but will also reduce emissions (CO2, SOx, NOx and Particulate Matter) commensurately which should result in some emissions credit trading value.
In addition to providing adequate oil film thickness to prevent metal-to-metal contact, lubricants for these engines are designed to cope with a variety of other stresses, including neutralizing acids formed by the combustion of fuels containing sulfur to minimize corrosive wear of the piston rings and cylinder liner, minimizing engine deposits formed by fuel combustion and by contamination of the lubricant with raw or partially burned fuel, resisting thermal/oxidation degradation of the lubricant due to the extreme heat in these engines, transferring heat away from the engine, etc.
A long term requirement is that the lubricant must maintain cleanliness within the high temperature environment of the engine, especially for critical components such as the piston and piston rings. Contamination of the engine oil in the engine by the accumulation in it of raw and partially burned fuel combustion products, water, soot as well as the thermal/oxidation degradation of the oil itself can degrade the engine cleanliness performance of the engine oil. Therefore, it is desirable for engine oils to be formulated to have good cleanliness qualities and to resist degradation of those qualities due to contamination and thermal/oxidative degradation.
There is a need for an improved marine diesel oil formulation and methods of making and using such formulations for improving fuel efficiency and reducing emissions of marine diesel engines in combination with the other desired attributes described above.